Cytological and Biochemical Profile of Cerebrospinal Fluid from Meningitis Patients

BACKGROUND: The term Meningitis is used to describe an inflammatory infection of the membranes surrounding the brain and spinal cord, which occurs as either a primary disease or secondarily to disease in some other part of the body. The diagnosis is primarily confirmed by analyzing cerebrospinal fluid (CSF). Early diagnosis of the cause may be based on the cytological and biochemical parameters. Our objective was to determine the cytological and biochemical profile of CSF from meningitis patients.


Introduction
The CSF is a clear bodily fluid that occupies the space between the arachnoid mater (meninges) and the pia mater.It is formed in the choroid plexus by both filtration and active transport.It protects the brain from the sudden change in pressure, it maintains stable chemical environment and removes wastes products of cerebral metabolism [1].
CSF evaluation is the single most important aspect of the laboratory diagnosis of meningitis.Analysis of the CSF abnormalities produced by bacterial, mycobacterial, and fungal infections may greatly facilitate diagnosis and direct initial therapy.Basic studies of CSF that should be performed in all patients with meningitis include measurement of pressure, cell count and white cell differential; determination of glucose and protein levels; Gram's stain; and culture [2].
The inflammation by various pathogens induces anatomical and physiological changes in the meninges which are responsible for characteristic changes in the values of CSF from patients with meningitis.The loss of integrity of cerebral capillaries and thus, the loss of integrity of the blood-brain barrier results in leakage of protein into the CSF and increased migration of Polymorphonuclear (PMN) leukocytes into the CSF [3].
Normal CSF contains 0-5 lecukocytes/mm3 , mainly lymphocytes, though in neonates cell count is up to 30/mm 3 [4].WBC count of >500/mm 3 with a preponderance of neutrophils is characteristic of a bacterial meningitis, and a WBC count of >100/mm 3 with a preponderance of monocytes is characteristic of a viral meningitis a considerable pattern overlap is often found [5].CSF glucose levels are used to distinguish bacterial meningitis (where it is usually decreased, usually <40 mg/dl) from aseptic meningitis (where the glucose levels are usually unaltered) [5].Decreased CSF glucose results from changes in the physiological functioning of the choroid epithelium as well as from consumption by bacterial pathogens and leukocytes [6].Chemically meningitis can be differentiated from bacterial meningitis by CSF glucose levels (<10 mg/dL) and CSF WBC values (>7500 cells/mm 3 ) [7].
Proteins are largely excluded from the CSF by the blood -CSF barrier.Protein gaining access to the CSF primarily reaches the CSF by transport within pinocytotic vesicles traversing capillary endothelial cells [1].Protein level greater than 200 mg/dL, is highly significant for bacterial meningitis indicating disruption of the bloodbrain or the blood-CSF barrier [8].
This study aims to look at the changes in the cytological and biochemical value of CSF for the diagnosis of meningitis.

Across sectional study was carried out at the Emergency laboratory in Tribhuvan University
Teaching Hospital (TUTH) from March to August 2014.Total 356 CSF samples were collected from patients clinically suspected of meningitis.The samples were processed microscopically and microbiologically to determine cytological and biochemical and microbiological parameters for diagnosing meningitis.The TLC were counted by Neubauer counting chamber method and differential leukocytes count (DLC) was by Wright's staining.The level of protein and glucose was determined by using Biochemistry Automatic Analyzer (Erba XL-200).
The specimens were cultured on Chocolate agar (CA), Blood agar (BA), MacConkey agar (MA), Mannitol salt agar (MSA), Nutrient agar (NA) and Sabouraud Dextrose agar (SDA).For bacterial isolates, BA and CA plates were incubated in candle jar (5-10% CO 2 ) at 37 o C for overnight.MA plates were incubated at 37 o C in incubator for overnight.SDA plates were used for culture of fungal isolates and incubated at 37 o C for 2-3 days.

Results
Among the total 356 processed CSF samples, there was a slight male dominance in the sex ratio (1.3:1) with males contributing 56.5% and females 43.5% (Table 1).The mean age of the patients was 27.8 years.
Among the total processed specimen (N=356), only 16(4.5%) cases were known to have laboratory confirmed cases of meningitis with the help of CSF culture results.
And no isolate was from samples having normal cell count range (Table 2).
The mean value of TLC was found to be more (337.3cells/mm 3 ) in bacterial meningitis compared to fungal meningitis (11.7 cells/mm 3 ).Neutrophils were predominant in bacterial meningitis whereas lymphocytes were predominant in fungal meningitis (Table 3).

BIOCHEMICAL PROFILE
The isolation rate of pathogens was highest (13 out of 72, 18.1%) in the CSF samples having glucose level <40 mg/dL.Similarly highest number of pathogens (13 out of 150, 8.7%) were isolated from the CSF samples having protein level >45 mg/dL.

Table 1 .
Age and Sexwise Distribution of Suspected Cases of Meningitis

Table 2 .
TLC of Total CSF Specimen and Culture Positive Isolates